1. Technical Field of the Invention
Embodiments in accordance with the invention relate generally to laser-based transmitters, and more specifically to interconnecting electroabsorption modulated lasers (EML) with a driver integrated circuit (IC).
2. Description of Related Art
Electroabsorption modulated laser (EML) based Coarse Wavelength Division Multiplexed (CWDM) transmitters achieve data rates of 10 Gb/s and greater per channel. An EML typically includes a monolithically-integrated continuous-wave distributed feedback (DFB) laser and an electroabsorption modulator. A typical EML CWDM transmitter module includes: (1) an array of EMLs, with each EML operating at a different wavelength; (2) a multi-channel driver integrated circuit (IC) to drive the array of EMLs at a desired data rate; (3) an optical multiplexer to combine the array's optical outputs; (4) and focusing optics to couple multiplexer outputs to an optical fiber.
It is desirable that the EML CWDM transmitter module achieve as great a maximum data rate as possible. However, electrical interconnections between a multi-channel driver IC and an EML array limit the maximum achievable data rate of the EML CWDM transmitter module. The maximum data rate is often lower than desirable due to high-speed electrical signal induced inductance. The inductance can be reduced by shortening the interconnections between the IC and the EML array.
In a typical arrangement, making the interconnections between the IC and the EML array sufficiently short is difficult. The optical multiplexer is placed near a front of an EML array facet where light emerges from the EML array. The driver IC is typically placed adjacent to a back facet of the EML array. In this arrangement, a high-speed portion of the EML array is near the front facet. Since the high-speed portion of the EML array is near the front facet, an interconnection from the back of the EML array to the driver IC is considered lengthy. Such an arrangement is not preferable for high-data-rate applications.
Thermal management issued are introduced when the interconnection length is shortened. Data rate can be maximized between an EML and a driver IC by directly flip-chip bonding the EML array onto the driver IC. Although a sufficiently-short interconnection length is achieved by directly flip-chip bonding the EML array onto the driver IC, thermal management of the combination becomes difficult because a driver-IC-EML-array assembly so flip-chip bonded must be cooled down to within the EML array's operating temperature.
Conflicting requirements of low interconnection-induced inductances and high thermal resistance make the high-speed interconnection between an EML array and a driver IC difficult. What is needed is an interconnection between a driver IC and the EML array resulting in low interconnection-induced inductances, high thermal resistance, and low space consumption.